Physical Therapy Assistant Practice Exam 2025 - Free PTA Practice Questions and Study Guide

The upper trapezius is the muscle that assists with the elevation of the scapula and is innervated by the accessory nerve. This muscle plays a key role in shrugging the shoulders and is crucial for movements that require lifting the shoulders, such as overhead activities. The accessory nerve, also known as cranial nerve XI, provides motor innervation specifically to the upper trapezius and sternocleidomastoid muscles.

In the context of the other muscles mentioned, the lower trapezius primarily aids in scapular depression and upward rotation, while the rhomboids are primarily responsible for scapular retraction and elevation but do not have accessory nerve innervation. Furthermore, the serratus anterior is mainly involved in the protraction and upward rotation of the scapula, innervated by the long thoracic nerve instead. Therefore, the specific role of the upper trapezius in scapula elevation and its unique innervation by the accessory nerve clearly highlight why it is the correct answer.